1. FIELD OF THE INVENTION
This invention relates to a lubricating oil composition particularly suitable as a railway diesel engine oil.
2. PRIOR ART DESCRIPTION
The prior art to which this invention relates evidences activity and includes coassigned U.S. Pat. Nos. 3,969,235; 3,474,035; 3,528,917; and 3,761,414, as well as U.S. Pat. Nos. 7,010,106; 3,377,281; 3,367,867; 4,016,093; 3,562,159 and 3,775,321.
Over the past several years the railroad engine manufacturers were required to modify their new engines, as well as the older engines which were being overhauled, to meet certain environmental criterion. The engine modifications caused lube oil drain periods to be reduced. Instead of the normal six-month drain periods with 6 TBN (Total Base Number) oils, the oil must now be drained at about 3 months. To extend the oil drain periods to their original 6-month interval the engine builders are now recommending higher TBN oils (about 10). The 10 TBN oils are usually more expensive than 6 TBN oils.
In a related coassigned patent application, Ser. No. 754,658, filed Dec. 27, 1976, now U.S. Pat. No. 4,169,799, it is disclosed that the combination of components consisting of a 2:1 overbased calcium salt of a sulfurized alkyl phenolate, a alkenylsuccinimide and a chlorinated hydrocarbon in a mineral oil base stock mixture provides a 10 TBN product which outperforms commercial blends in oxidative stability, corrosion control and alkaline retention and is competitive economically with them. However, it was necessary to use a chlorinated hydrocarbon in the above formulation to maintain the excellent silver frictional characteristics of the oil.